Lithium ion (and other) batteries generally employ a liquid electrolyte which is hazardous to humans and to the environment and which can be subject to fire or explosion. Liquid electrolyte batteries are hermetically sealed in a steel or other strong packaging material which adds to the weight and bulk of the packaged battery. A new innovation is the pouch cell, which has been used in lightweight batteries, but these have not seen widespread acceptance.
Conventional liquid electrolyte also suffers from the build-up of a solid interface layer at the electrode/electrolyte interface which causes eventual failure of the battery. Conventional lithium ion batteries can also exhibit slow charge times on the order of hours. In addition, the batteries suffer from a limited number of recharges since the chemical reaction within the battery reaches completion and limits the re-chargeability because of corrosion and dendrite formation. The liquid electrolyte also limits the maximum energy density. The electrolyte starts to break down at about 4.2 volts. New industry requirements for battery power are often 4.8 volts and higher which cannot be achieved by present liquid electrolyte lithium ion cells. There have been developments in both spinel structures and layered oxide structures which have not been deployed due to the limitations of the liquid electrolyte. Also, lithium ion batteries with liquid electrolytes suffer from safety problems with respect to flammability of the liquid electrolyte.
In a conventional lithium ion battery having a liquid electrolyte there is also a need for a separator in the liquid electrolyte. The separator is a porous structure which allows for ions to flow through it, and blocks electrons from passing through it. The liquid electrolyte battery usually requires a vent to relieve pressure in the housing, and in addition, such conventional batteries usually include safety circuitry to minimize potentially dangerous over-currents and over-temperatures. FIGS. 1 and 2 show schematics and general reactions in such conventional lithium ion batteries.